This invention relates to a circuit interrupter, and more particularly to a circuit interrupter which comprises a toggle link mechanism composed of an operating handle and a link, a latch lever for engaging and releasing a movable member and the link, and an overcurrent trip means.
A conventional circuit interrupter of this kind is constructed as shown in FIGS. 1 and 2. FIG. 1 is a sectional side view illustrating the OFF state of the conventional circuit interrupter and FIG. 2 is an exploded perspective view showing the main portion of the circuit interrupter. In the figures, 1 is a base made of an electrically insulating material, 2 is a handle pivotally supported around a shaft 101 which is a portion of the base 1, 3 is a torsion spring mounted on the shaft 101, its one end engaging said base 1 and the other end engaging the handle 2 to bias the handle 2 in the counterclockwise direction.
A U-shaped pin 4 which is a link having one leg rotatably inserted into a hole (not shown) formed in the inner end 201 of the handle 2, 5 is a movable member pivotally supported by a shaft 6 supported by an elongated hole 102 formed in the base 1, the movable member having a pair of first and second latch surfaces 5a and 5b at one of the pivot end portions. A latch lever 7 pivotally supported by the shaft 6 and is usually biased by a torsion spring 8 in the direction opposite to the direction in which the movable member 5 is biased and has a latch portion 7a for usually holding the other end of the link 4 together with the latch surfaces 5a and 5b.
A shaft 11 is mounted on the movable member 5, a movable contact 12 is secured at one end of the movable member 5, a shaft 13 is mounted on the base 1, a tension spring 14 is disposed between the shaft 13 and the shaft 1, a stationary member 15 is fixed on the base 1, a stationary contact 16 is secured on the stationary member 15 opposite to the movable contact 12, a coil 17 has one end which is electrically connected to the stationary contact member 15, and a terminal 18 is electrically connected to the coil 17 for connecting thereto an external conductor (not shown) by a wire catcher 19 and a screw 20.
A yoke 21 is mounted on the base 1 for forming a magnetic path, a plunger 22 is attracted to the left in the figure against the spring force of the compression spring 23 when the coil 17 is energized, and the coil 17 is wound around a bobbin 24, through the hollow portion of which the plunger 22 loosely extends. A rod 25 is driven to the left in the figure when the plunger 22 is attracted, a flexible copper wire 26 is electrically connected at one end to the movable member 5, and the other end of the flexible copper wire 26 is electrically connected to a bimetal 27, one end of the bimetal 27 being secured to a terminal 28, for connecting an external conductor (not shown) by a wire catcher 29 and a screw 30. An adjusting screw 31 is threaded into the terminal 28, an insulating tube 32 is disposed on the bimetal 27, an arc runner 33 is secured at one end to the terminal 28 and its other end is fitted into the groove in the base 1, side plates 34 are disposed in parallel to the moving direction of the arc on both sides of the arc runner 33, an arc extinguishing chamber 35 is for extinguishing an arc generated between the movable contact 12 and the stationary contact 16 and in which a plurality of grids 36 are supported at predetermined intervals by a pair of side plates 37.
As apparent from the foregoing description, when the circuit interrupter is in either an OFF state as shown in FIG. 1 or an ON state as shown in FIG. 3, the link 4 is held by the latch surfaces 5a and 5b of the movable member 5 and the latching portion 7a of the latch lever 7. When the handle 2 of the circuit interrupter shown in FIG. 1 is turned in the righthand direction (O operation) from the OFF state, the toggle link mechanism formed by the inner end 201 of the handle 2 and the link 4 straightens passing over the dead point, thereby causing the movable member 5 to rotate counterclockwise about the shaft 6, and the movable contact 12 engages the stationary contact 16, providing the ON state shown in FIG. 3. Then, when the handle 2 is rotated in the lefthand direction (OFF operation), the toggle mechanism formed by the inner end 201 of the handle 2 and the link 4 collapses passing over the dead point to rotate the movable member 5 around the shaft 6 in the clockwise direction to separate the movable contact 12 from the stationary contact 16 bringing about the OFF state shown in FIG. 1.
Next, when a relatively small overcurrent such as an overload current flows, the bimetal 27 in the state shown in FIG. 3 deflects due to its Joule's heat to press the lever 7 by the tip portion of the bimetal 27 to release the engagement of the other end of the lever 7, to rotate the movable member 5 clockwise about the shaft 6 by the biasing force of the tension spring 14 to separate the movable contact 12 from the stationary contact 16, to a state at the instant of tripping as shown in FIG. 4. Thereafter, the biasing force of the torsion spring 3 causes the rotation of the handle 2 in the counterclockwise direction, positioning the other end of the link 4 between the latch surfaces 5a and 5b and the latching portion 7a to hold the link 4 by the latch surfaces 5a and 5b and the latching portion 7a, providing the OFF state shown in FIG. 1. That is, an automatic reset is achieved. The above-described tripping is achieved with a time delay.
On the other hand, when a large overcurrent such as a shortcircuiting current flows, the coil 17 is excited to attract the plunger 22 against the biasing force of the compression spring 23 to push out the rod 25, rotating the lever 7 in the clockwise direction about the shaft 6 to release the other end of the link 4. Thereafter, the operation is similar to the operation when an overload current achieves tripping. This tripping is achieved instantaneously.
With the conventional circuit interrupter as above described, since the latch lever 7 is mounted to the movable member 5 by a shaft 6, an impact force is directly transmitted to the movable member 5 from the rod 25 through the shaft 6 upon shortcircuiting, causing an instantaneous separation of the movable contact 12 from the stationary contact 16 to generate an electric arc therebetween and immediately reclosing, posing a problem of contact welding.
Also, since the movable member 5 electromagnetically repulses to separate together with the latch lever 7 when a shortcircuiting current increases, the time point at which the rod 25 pushes the latch lever 7 away from the movable member is delayed, resulting in a delay in tripping. That is, a problem arises which prevents quick interruption. The problem is severe at higher instantaneous trip current set values of a high current rating.